Over the past thirty years, asphalt has replaced concrete as the material of choice for paving roadways. Asphalt provides a smooth road surface that is easier to apply and easier to resurface than concrete. However, asphalt pavers generally cannot pave an entire road surface in a single pass and therefore joints must be formed between the previously placed asphalt and the newly placed asphalt being placed by the paver. It is at these joints that asphalt is most susceptible to failure as the "cold", previously placed, asphalt is not sufficiently heated by the hot asphalt from the paver to form a homogenous bond at the joint. These non-homogenous "cold joints" often will separate and create cracks, most usually in the center of two lane roads, which allows water to enter the pavement, migrate to the road base and, over a period of time, contribute substantially to base failure of the road.
To overcome this problem, the previously placed pavement joint, must be heated to approximately the same temperature as the new material that is being placed to provide the proper environment for thermal bonding. However, the chemical properties of asphalt make this a difficult task. First, asphalt is a petroleum based product and has a tendency to burn if overheated. Second, the mass and thermal conductivity of asphalt necessitate heating the asphalt for a significant period of time to raise the temperature of the entire asphalt layer to the desired bonding temperature. The combination of these properties makes traditional heating by propane torch, either hand-held or paver-mounted, an ineffective and dangerous exercise.
When paver-mounted heaters are used to preheat the asphalt, the temperature of the burning propane raises the temperature of the top layer of asphalt to its burning temperature well before the remainder of the asphalt layer has reached its desired bonding temperature. Thus, to avoid igniting the top of the asphalt layer, the paver must move before the entire layer is sufficiently heated, bonding the new hot asphalt to "warm" asphalt. This increases the adhesion somewhat, but does not provide the durability of a true "hot joint". When hand held heaters are used, the heat to the pavement may be cycled to allow proper heating of the entire layer. However, the risk of fire increases with this approach as the exposure of the heater to the pavement is controlled by the operator. In addition, the use of hand held heaters requires additional manpower and slows the paving process.
A method or apparatus for joining a newly paced layer of asphalt to a previously placed layer of asphalt that creates a durable and substantially homogenous "hot joint", that does not create a risk of fire, that does not require additional manpower, and that allows asphalt to be placed in a substantially continuous process, is not known in the art.